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Last updated September 11, 2019. 11 minute read

Chlamydia: symptoms, testing, treatment, and more

One of the reasons that chlamydia is so prevalent is that, in the majority of cases, it is asymptomatic. This means that people may not know they are infected with chlamydia, so they do not seek treatment and may continue to spread it. In fact, it’s estimated that only 10% of men and 5-30% of women experience symptoms.

Dr Mike Bohl Md Mph Written by Dr. Mike Bohl, MD, MPH
Reviewed by Dr. Tzvi Doron, DO

Reading about chlamydia may transport you back to your school days—you and 20 of your peers sitting in a classroom for an hour every week to learn about sexually transmitted infections (STIs). Early education about STIs is key to helping prevent their spread, but then once high school is over – something changes. STIs become a taboo topic and something that people may be nervous about bringing up to their healthcare provider. Information about STIs may also seem harder to find – of all the medical commercials you’ve seen on television, try to think about how many discuss STIs (although there was one 2018 Norwegian commercial that garnered some headlines). This can potentially lead to harmful outcomes. Multiple studies have found that the shame and stigma surrounding STIs can be a barrier to patients seeking out screening and treatment (Cunningham, 2009 and Morris, 2014). This is especially concerning for a condition like chlamydia, which can often be asymptomatic.


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What is chlamydia?

Chlamydia is an STI caused by the bacteria Chlamydia trachomatis. It was discovered in 1907 by Ludwig Halberstädter and Stanislaus von Prowazek while they were investigating patients with trachoma, a disease in which the inner eyelid becomes rough (Taylor-Robinson, 2017).

Very generally, the term “chlamydia” may refer to a group of bacteria in the genus chlamydia. One of the characteristics of these bacteria is that they are obligate intracellular organisms. Being an obligate intracellular organism means that the bacteria have to live inside the cells of the host they are infecting to reproduce.

When Halberstädter and von Prowazek first discovered the bacteria and saw that it lived inside human cells, they named it Chlamydozoa from the Greek chlamys, meaning cloak. They also initially thought they had discovered a virus or protozoan (a single-celled organism). However, further testing confirmed that chlamydia was a genus of bacteria that contained nine different species.

Chlamydia species that infect humans include Chlamydia pneumoniae (which causes pneumonia), Chlamydia psittaci (which causes a respiratory disease called psittacosis and comes from birds), Chlamydia abortus (which can cause fetal death), and Chlamydia trachomatis (the STI). Chlamydia trachomatis is further divided into subtypes called serovars. The exact number of serovars differs from source to source, but they are generally divided into:

  • Serovars A-C: Cause trachoma (roughening of the inner part of the eyelid).
  • Serovars D-K: Cause infection of the internal and external .genitalia, non-gonococcal urethritis (inflammation of the urethra that is not due to gonorrhea), proctitis (inflammation of the lining of the rectum), and conjunctivitis (a.k.a. pinkeye).
  • Serovars L1, L2, L3: Cause lymphogranuloma venereum (infection of the lymphatic system) and proctitis in men who have sex with men (MSM).

How common is chlamydia?

Chlamydia is the most common reportable bacterial infection in the United States. In 2017, 1.7 million cases of chlamydia were reported to the Centers for Disease Control and Prevention (CDC) (Hsu, 2019). This represents approximately 529 cases per 100,000 people. This is over three times the number of cases of gonorrhea reported in the same year. Since the majority of chlamydial infections are asymptomatic, it is assumed that the actual number of people infected with chlamydia is much higher than this. Rates of chlamydia are also increasing, with 2017’s numbers representing a 6.9% increase from 2016.

Typically, lymphogranuloma venereum (LGV) was found in tropical and subtropical regions of the world, including Africa, the Caribbean, India, and Southeast Asia and could infect heterosexuals. However, since 2003, outbreaks have been seen in North America and Western Europe. These outbreaks are primarily amongst MSM, 76% of which also have HIV (according to one study) (Ward, 2007).

What are the risk factors for getting chlamydia?

The risk factors for getting chlamydia include age, sex, race, and sexual activity.

  • Age: The prevalence of chlamydia is highest in people aged 14-24, with one study showing that the overall rate of infection in those aged 18-26 is 4.2% (Hsu, 2019).
  • Sex: Females are approximately twice as likely to be infected as males, with one estimate stating that 1 in 20 sexually active females aged 14-24 is infected with chlamydia (CDC, 2019). Having a condition known as cervical ectopy, which is when cells from the inside of the cervix are present on the outside of the cervix, can make infection with chlamydia more likely.
  • Race: The incidence of infection in African Americans is six times the incidence in whites, while the rate in Alaska Natives and American Indians is 3.8 times the incidence in whites. Combining both race and sex, the prevalence of chlamydial infection in African American women is 14% (Hsu, 2019).
  • Sexual activity: Chlamydia is spread through sexual activity, so being sexually active, having multiple partners, and not using barrier protection (such as condoms) are all risk factors for acquiring the infection. MSM are also at increased risk of being infected with chlamydia.

How is chlamydia passed from one person to another?

Chlamydia is spread through sexual contact. This means that coming into contact with the anus, mouth, penis, or vagina of somebody who is infected may cause an individual to become infected as well. Anal, oral, and vaginal sex can all spread the infection even if ejaculation does not occur. It is not possible to spread chlamydia through kissing or sharing cups with somebody who has chlamydia.

Chlamydia can also be spread from mother to child during birth. This may cause pneumonia or conjunctivitis in the newborn.

What are the signs and symptoms of chlamydia?

One of the reasons that chlamydia is so prevalent is that, in the majority of cases, it is asymptomatic. This means that people may not know they are infected with chlamydia, so they do not seek treatment and may continue to spread it. In fact, it’s estimated that only 10% of men and 5-30% of women experience symptoms. When infection with chlamydia does cause symptoms or complications, it is known as a sexually transmitted disease (STD).

Chlamydia has different symptoms depending on the part of the body that is infected.

Everybody can have the following infections:

  • Infection of the urethra (urethritis): This can lead to increased frequency of urination and pain or burning with urination (dysuria). In those with a penis, urethritis can lead to penile discharge and an itchy feeling at the opening of the penis. The discharge typically begins 5-10 days after exposure and is watery. It is low in volume, so it may only be noticeable when milking the penis or when stains show up on underwear. This is in contrast to the discharge seen with a gonorrheal infection, which is typically thicker and greater in volume.
  • Infection of the lymphatic system (LGV): This can start with a non-painful genital ulcer and lead to swelling and pain of the lymph nodes in the groin.
  • Infection of the lining of the rectum (proctitis): Proctitis in females is typically asymptomatic. Proctitis in MSM is generally caused by the LGV serovars of chlamydia and leads to rectal pain, discharge, bleeding, constipation, and the sensation of always needing to go to the bathroom (tenesmus).
  • Infection of the throat (pharyngitis): Although it is not considered a common cause of sore throat, chlamydia can infect the throat.
  • Infection of the outer layer of the eyes (conjunctivitis): This may cause redness, tearing, and irritation of the infected eye or eyes.

Infections and symptoms specific to biological males include:

  • Infection behind the testes (epididymitis): The epididymis is a coil of tubes attached to the back of the testicle. Infection of this area can lead to one- or two-sided scrotal swelling and pain.
  • Infection of the prostate (prostatitis): It is thought that infection with chlamydia could be one cause of chronic prostatitis (long-term inflammation of the prostate). This causes pain with urination, pain with ejaculation, pelvic pain, incontinence, and difficulty urinating.

Infections and symptoms specific to biological females include:

  • Infection of the cervix (cervicitis): This rarely presents with symptoms, but when they do occur, they are nonspecific. Symptoms may include vaginal discharge, bleeding between menstrual periods, and bleeding after sexual activity. These symptoms typically begin 7-14 days after exposure.
  • Ascending infection: If untreated, chlamydia can spread from the cervix to the rest of the reproductive system, even affecting other organs in the abdomen. This can cause pelvic pain and abdominal pain and is one of the complications of untreated chlamydia.

What are the complications of untreated chlamydia?

Chlamydia can be easily treated with antibiotics. However, because it is often asymptomatic, many people may go without treatment. Some may also go without treatment even if they have symptoms because of a lack of access to healthcare or because of perceived stigma surrounding their condition. Luckily, many cities have free clinics or reduced-cost clinics where the amount you pay depends on your income. These locations offer a judgment-free way for many people to receive treatment easily.

Some people still may not receive treatment, which can lead to complications as the infection spreads. In everybody, untreated chlamydial infection increases the risk of acquiring human immunodeficiency virus (HIV).

Approximately 1% of men who have urethritis go on to develop a type of arthritis called reactive arthritis. This causes pain and swelling in the joints, typically affecting the knees and the feet (but it could be anywhere). In some cases, urethritis and reactive arthritis also occur with conjunctivitis or uveitis, which is inflammation of part of the eye that can cause blurred vision. This triad of symptoms is called Reiter’s syndrome. Chlamydia is not the only organism that causes Reiter’s syndrome, but it is one of the most common. Treatment involves receiving antibiotics for the infection and nonsteroidal anti-inflammatory drugs (NSAIDs) for the arthritis. If arthritis is more advanced, steroids or medications used to treat rheumatoid arthritis may be necessary.

In biological females, chlamydia can spread from the cervix to the rest of the reproductive system, including the uterus, fallopian tubes, and ovaries. This causes a condition called PID, which is associated with pelvic pain and abdominal pain. In some, PID may also be asymptomatic. PID can lead to severe complications, including scarring of the fallopian tubes, infertility, and ectopic pregnancy. An ectopic pregnancy is a pregnancy in which the egg implants somewhere other than the uterus. This can potentially lead to a rupture, which is a medical emergency and can even be fatal. While PID may also occur from a gonorrhea infection, the complications of PID occur more frequently when caused by chlamydia. This makes chlamydia and gonorrhea two important causes of preventable infertility amongst women. If already pregnant, chlamydia can increase the risk of having a preterm delivery.

PID can also spread even higher in the abdomen, causing inflammation of the lining of the liver. This is called perihepatitis or Fitz-Hugh-Curtis syndrome and can cause pain on the right side of the abdomen below the ribcage. As it advances, Fitz-Hugh-Curtis can cause scarring and adhesions in the abdomen, which may need to be removed with surgery.

How is chlamydia diagnosed?

Diagnostic testing for chlamydia can be done either to confirm a diagnosis in somebody who has symptoms or as a screening test in somebody who does not have symptoms. The United States Preventive Services Task Force (USPSTF) currently recommends screening for chlamydia and gonorrhea in sexually active females under the age of 25 (USPSTF, 2019). For those who are older, screening is recommended in those who are at higher risk of infection (i.e., those who participate in high-risk sexual behavior such as unprotected sex and sex with multiple partners). It is recommended that MSM be screened as frequently as every 3-6 months.

Multiple tests can be done to diagnose chlamydia, but the best option is the nucleic acid amplification test (NAAT). This is the test of choice because it is the most sensitive, which means it very easily detects chlamydia and will lead to the fewest false negatives. NAAT can be done once a sample is obtained. A urine sample or a vaginal swab can be obtained depending on if a patient has a penis or vagina. Individuals should also be swabbed everywhere they may be at risk of infection, which is determined by the type of sex the individual has. If an individual engages in oral sex and pharyngeal chlamydia is suspected, a throat swab should be obtained. Similarly, if an individual engages in receptive anal intercourse and rectal chlamydia is suspected, a rectal swab should be obtained.

How is chlamydia treated?

Chlamydia can be easily treated with antibiotics. In some cases, an individual may be presumptively treated even before the test results come back. This is especially likely if symptoms are present or if a sexual partner has tested positive for chlamydia.

Treatment involves a one-time dose of an antibiotic called azithromycin (brand name Zithromax). This is taken orally and is often available in the clinic. Sometimes, an antibiotic called doxycycline (brand name Vibramycin) is used instead and is prescribed for a 7-day course. If epididymitis is suspected, doxycycline is prescribed for a 10-day course. If PID is suspected, doxycycline is prescribed for a 14-day course (although additional interventions may be necessary depending on the severity). If LGV is suspected, doxycycline is prescribed for a 21-day course. Doxycycline can cause sensitivity to the sun (photosensitivity) so if you are taking doxycycline, make sure to wear sunscreen and do your best to avoid the sun while on the medication.

Many times, patients will also be given a one-time injection of an antibiotic called ceftriaxone (brand name Rocephin). Ceftriaxone is used to treat gonorrhea, which frequently infects individuals along with chlamydia.

Individuals who are being treated for chlamydia should refrain from having sex for seven days from when they start taking antibiotics. The reinfection rate for chlamydia is high, and having sex right away may continue to spread the disease and may contribute to reinfection. With this in mind, individuals should also get re-tested after three months to make sure reinfection has not occurred. It is also recommended that all sexual partners from within 60 days of symptoms occurring are contacted to let them know that they should be tested and treated as well.

In 2016, the World Health Organization (WHO) released new guidelines for the treatment of chlamydia, gonorrhea, and syphilis. This was prompted by a growing concern regarding antibiotic-resistant bacteria (WHO, 2016). Antibiotic-resistant bacteria are bacteria that have evolved in a way that makes the antibiotics we usually use on them less effective. There has been much concern about the emergence of antibiotic-resistant gonorrhea (sometimes called “super drug-resistant gonorrhea” or just “super gonorrhea”) in Europe and the possibility that a strain may develop that antibiotics cannot cure. Some chlamydia that is resistant to antibiotics has begun emerging in parts of the world, but, at the moment, it is still treatable. Nonetheless, the best way to avoid getting a drug-resistant strain of chlamydia is to avoid getting chlamydia altogether.

How can chlamydia be prevented?

The most effective way to prevent chlamydia is to abstain from sexual activity or to remain in a monogamous relationship with somebody who does not have chlamydia. If you are going to participate in sexual activity, the best way to avoid chlamydia is to practice safe sex. This involves using a polyurethane or latex condom or other barriers that entirely prevent direct contact during anal, oral, and vaginal sex. Keep in mind that just because something is a contraceptive does not mean it prevents STIs as well. Birth control medications, spermicidal lubricants, and other incomplete barriers like the diaphragm do not protect against STIs.

Some people may take a medication known as Truvada for PrEP. PrEP stands for Pre-Exposure Prophylaxis and is taken by individuals who are HIV negative to prevent infection with HIV. Even though PrEP is effective at preventing HIV, it does not prevent other STIs like chlamydia.

Is there a vaccine for chlamydia?

Recently, a study was published regarding the phase 1 trial of a vaccine for chlamydia (Abraham, 2019). A vaccine is a treatment that can be given to people that sensitizes their body to a certain disease. This helps protect against acquiring that specific disease in the future. Phase 1 trials are done in very small groups of people (in this case, 40 women) and are intended to assess whether or not the intervention is safe and what its side effects are. In this study, the potential vaccine for chlamydia was deemed to be safe and well-tolerated, which means it may move on to the next phase of clinical trial. So what does this mean? For now, there is no vaccine for chlamydia, however there may be one in the coming years if clinical trials show it to be safe and effective.


  • Chlamydia is the most common reportable bacterial infection in the United States.
  • Rates of chlamydia are also increasing, with 2017’s numbers representing a 6.9% increase from 2016.
  • Chlamydia can be easily treated with antibiotics. However, because it is often asymptomatic, many people may go without treatment.
  • Left untreated, chlamydia can cause pelvic inflammatory disease (PID), which can lead to severe complications, including scarring of the fallopian tubes, infertility, and ectopic pregnancy. 
  • Chlamydia can cause urethritis. Approximately 1% of men who have urethritis go on to develop reactive arthritis, causing pain and swelling in the joints.